Scheduler fails with "ActiveRecord::ConnectionTimeoutError: could not obtain a connection from the pool within 5.000 seconds (waited 5.000 seconds); all pooled connections were in use>"

I had this issue as well when pulling the zammad/zammad-docker-compose project.

Turns out that when updating the zammad-docker-compose project with the settings for Zamma 6.3.0 specifically:

POSTGRESQL_OPTIONS=?pool=50

It is not being propagated into the docker-compose.yml. For me changing: POSTGRESQL_OPTIONS: in docker-compose.yml to POSTGRESQL_OPTIONS: ${POSTGRESQL_OPTIONS} fixed it.